Hydraulic valve with pressure limiter function

ABSTRACT

A hydraulic system includes first and second valve assemblies connected to a common pump. The first valve assembly includes a main valve housed inside a manifold. A pressure compensator valve maintains a constant pressure drop across a variable orifice of the main valve. A pressure limiter valve is in communication with the main valve and the pressure compensator valve, and allows an actuator connected to the first valve assembly to operate independently of the second valve assembly so that fluid flow to a work port of the first valve assembly is not interrupted by operation of the second valve assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of Indian Provisional PatentApplication Serial No. 201811001394, entitled HYDRAULIC VALVE WITHPRESSURE LIMITER FUNCTION, filed on Jan. 12, 2018, the disclosure ofwhich is hereby incorporated by reference in its entirety.

BACKGROUND

Hydraulic systems used in various applications often include variousvalve assemblies each having different variable requirements and eachoperating its own actuator under different operating conditions. A loadsensing compensator can be used to tailor the operation of a hydraulicpump to meet the variable flow requirements of a given hydraulic systembased on load sense pressure. However, the inlet pump pressure receivedby each valve assembly is based only on the highest load sense pressuresensed by the load sensing compensator. Thus, inlet pump pressuresupplied to each valve assembly is the same even though the variousvalve assemblies may be operating different actuators under differentload pressures. Improvements in pump flow management in a hydraulicsystem having multiple valve assemblies are desired.

SUMMARY

The disclosed technology relates generally to a valve assembly forconnecting to a pump having load sensing functionality. In certainexamples, the pump is a variable displacement pump. In other examples,the pump is a fixed displacement pump having an inlet pressurecompensator.

In one aspect, the valve assembly comprises: a manifold; a main valvehoused inside the manifold, the main valve having a variable orifice; apressure compensator valve adapted to maintain a constant pressure dropacross the variable orifice and to communicate fluid from the variableorifice to a work port; and a pressure limiter valve in communicationwith the main valve and the pressure compensator valve. The pressurelimiter valve being biased by a threshold relief pressure and having apilot surface that receives a local load sense pressure from the workport. The pressure limiter valve drains fluid from the pressurecompensator valve to tank when the local load sense pressure overcomesthe threshold relief pressure of the pressure limiter valve. Thepressure limiter valve maintains flow to the work port when the valveassembly is part of a hydraulic system having multiple valve assemblies,and at least one other valve assembly of the multiple valve assemblieshas a higher threshold relief pressure and is operating under a higherload sense pressure than the valve assembly.

In some examples, the pressure limiter valve includes a spool moveablebetween a first position and a second position. The first positiondirects fluid from the variable orifice of the main valve to a pilotsurface of the pressure compensator valve, and the second positiondrains fluid from the pilot surface of the pressure compensator valve totank. The pilot surface of the pressure limiter valve is on a first sideof the spool, and a biasing element is positioned next to an oppositesecond side of the spool for biasing the spool into the first positionby the threshold relief pressure. The spool slides into the secondposition when the local load sense pressure received by the pilotsurface of the pressure limiter valve overcomes the threshold reliefpressure.

In certain examples, the pressure limiter valve is a two way twoposition valve having a spool moveable between a closed position and anopen position, the spool having a pilot surface that receives the localload sense pressure as a pilot pressure. The local load sense pressuremoves the spool of the pressure limiter valve from the closed positionto the open position. The closed position blocks fluid from draining totank, and the open position drains fluid to tank.

In certain examples, the pressure limiter valve is a three way twoposition valve having a spool moveable between a first position and asecond position, the spool having a pilot surface that receives thelocal load sense pressure as a pilot pressure. The local load sensepressure moves the spool of the pressure limiter valve from the firstposition to the second position. The first position communicates fluidto a pilot surface of the pressure compensator valve, and the secondposition drains fluid to tank. In some examples, the pilot surface ofthe pressure limiter valve has a rounded or conical shape.

In another aspect, the disclosed technology relates to a hydraulicsystem comprising: a pump; a load sensing compensator mounted to thepump; a first valve assembly housed in a manifold and connected to thepump and to a first actuator, the first valve assembly adapted tocommunicate a first load sense pressure to the load sensing compensator,the first valve assembling including: a main valve having a variableorifice; a pressure compensator valve adapted to maintain a constantpressure drop across the variable orifice and to communicate fluid fromthe variable orifice to a work port; and a pressure limiter valve incommunication with the main valve and the pressure compensator valve.The pressure limiter valve being biased by a first threshold reliefpressure, and includes a pilot surface that receives the first loadsense pressure from the work port. The pressure limiter valve drainsfluid from the pressure compensator valve to tank when the first loadsense pressure overcomes the threshold relief pressure. The hydraulicsystem further includes a second valve assembly housed in a separatemanifold and connected to the pump and to a second actuator. The secondvalve assembly is adapted to communicate a second load sense pressure tothe load sensing compensator. The second valve assembly includes: a mainvalve having a variable orifice; a pressure compensator valve adapted tomaintain a constant pressure drop across the variable orifice of themain valve; and a pressure relief valve biased by a second thresholdrelief pressure. In the hydraulic system, flow to the work port of thefirst valve assembly is maintained when the second threshold reliefpressure is higher than the first threshold relief pressure and thesecond load sense pressure is higher than the first load sense pressure.

In some examples, the pressure limiter valve is a two way two positionvalve that receives the first load sense pressure as a pilot pressure.The first load sense pressure moves the position of the pressure limitervalve from a closed position to an open position. The closed positionblocks fluid from draining to tank, and the open position drains fluidto tank.

In certain examples, the pressure limiter valve is a three way twoposition valve that receives the first load sense pressure as a pilotpressure. The first load sense pressure is adapted to move the positionof the pressure limiter valve from a first position to a secondposition. The first position communicates fluid to a pilot surface ofthe pressure compensator valve, and the second position drains fluid totank. In some examples, the pilot surface of the pressure limiter valvein the first valve assembly has a rounded or conical shape.

In another aspect, the disclosed technology relates to a valve assemblyfor connecting to a pump having load sensing functionality, the valveassembly comprising: a manifold; a main valve housed inside themanifold, the main valve including: a variable orifice having an openingproportional to a position of a spool inside the main valve; a pressurecompensator valve adapted to maintain a constant pressure drop acrossthe variable orifice of the main valve, the pressure compensator valveincluding: a spool being moveable between at least an open position anda closed position, the closed position blocks fluid from the variableorifice of the main valve, the open position communicates fluid from thevariable orifice to a work port, the work port adapted to connect to anactuator, the spool having a pilot surface on a first side opposite asecond side of the spool; and a biasing element positioned inside abiasing chamber next to the second side of the spool for biasing thespool into the closed position, the biasing chamber adapted to receive aload sense pressure from a second valve assembly via a load sense line,the load sense pressure applying an additional biasing force for movingthe pressure compensator valve into the closed position; and a pressurelimiter valve in fluid communication with the main valve and thepressure compensator valve, the pressure limiter valve including: aspool moveable between at least a first position and a second position,the first position directs fluid from the variable orifice of the mainvalve to the pilot surface of the spool of the pressure compensatorvalve, the second position drains fluid from the pilot surface of thespool of the pressure compensator valve to tank, the spool of thepressure limiter valve having a pilot surface on a first side of thespool opposite a second side of the spool, the pilot surface adapted forreceiving a local load sense pressure from the work port; and a biasingelement positioned next to the second side of the spool for biasing thespool into the first position by a threshold relief pressure, the spoolbeing adapted to move into the first position when the local load sensepressure received by the pilot surface overcomes the threshold reliefpressure. The pressure limiter valve maintains flow to the work portwhen the valve assembly is part of a hydraulic system having multiplevalve assemblies, and when at least one other valve assembly of themultiple valve assemblies has a threshold relief pressure that is higherthan the threshold relief pressure of the pressure limiter valve, andthe at least one other valve is operating under a load sense pressurethat is higher than the load sense pressure of the valve assembly.

In certain examples, the pressure limiter valve is a two way twoposition valve. In other examples, the pressure limiter valve is a threeway two position valve. In some examples, the pilot surface of thepressure limiter valve has a rounded or conical shape. In some examples,a hydraulic system comprises multiple valve assemblies, wherein at leastone valve assembly is the valve assembly describe above.

A variety of additional aspects will be set forth in the descriptionthat follows. These aspects can relate to individual features and tocombinations of features. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory only and are not restrictive of the broad concepts uponwhich the embodiments disclosed herein are based.

DRAWINGS

FIG. 1 illustrates fluid flow in two post compensated valve assembliesincluded in a hydraulic system, each valve assembly having a local loadsense relief valve.

FIG. 2 depicts a hydraulic circuit in accordance with a first example ofthe present disclosure, the hydraulic circuit having multiple valveassemblies each connected to an actuator and each having a two way twoposition pressure limiter valve.

FIG. 3 depicts a structural arrangement of the hydraulic circuit of FIG.2.

FIG. 4 depicts the hydraulic circuit of FIG. 2 when a work load pressurein a first valve assembly is less than a threshold relief pressure ofthe pressure limiter valve.

FIG. 5 depicts the hydraulic circuit of FIG. 2 when a work load pressurein a first valve assembly is greater than a threshold relief pressure ofthe pressure limiter valve.

FIG. 6 depicts an alternative example of a hydraulic circuit inaccordance with another example of the present disclosure, the hydrauliccircuit having multiple valve assemblies, one valve assembly connectedto an actuator and having a three way two position pressure limitervalve.

FIG. 7 depicts a structural arrangement of the hydraulic circuit of FIG.6.

FIG. 8 depicts the hydraulic circuit of FIG. 6 when a work load pressurein a first valve assembly is less than a threshold relief pressure ofthe pressure limiter valve.

FIG. 9 depicts the hydraulic circuit of FIG. 6 when a work load pressurein a first valve assembly is greater than a threshold relief pressure ofthe pressure limiter valve.

FIG. 10 illustrates fluid flow in two valve assemblies in a hydraulicsystem in accordance with the present disclosure.

FIG. 11 depicts alternative arrangements for a pilot surface of a threeway two position pressure limiter valve depicted in FIGS. 7-9.

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary aspects of thepresent disclosure that are illustrated in the accompanying drawings.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like structure.

A hydraulic system may include multiple valve assemblies each connectedto a pump and each operating its own actuator under a different loadsense pressure. In FIG. 1, the flow A in a first valve assembly iscompared with the flow B in a second valve assembly as the inlet pumppressure P from the pump increases. The inlet flow F is shown asremaining relatively constant while the inlet pump pressure P of thepump increases. The load sense pressure LA of the first valve assemblyis shown as remaining relatively constant as the inlet pump pressure Pincreases. However, the flow A in the first valve assembly begins todecrease when the inlet pump pressure P begins to increase andeventually reaches zero before the flow B in the second valve assemblybegins to decrease. This may be due to a local relief valve in the firstvalve assembly having a threshold relief pressure that is less than thethreshold pressure of a local relief valve in the second valve assembly.Since each local relief valve opens and closes based on the same inletpump pressure from the pump, the flow A in the first valve assembly iscut off before the flow B in the second valve assembly is cut off. Thismay occur even though the work port pressure in the first valve assemblyhas not exceeded the threshold relief pressure of the local relief valvein that assembly. Thus, operation of an actuator connected to the firstvalve assembly is affected which may result in energy loss in thehydraulic system having the first and second valve assemblies.

As shown in FIGS. 2 and 3, a hydraulic system 10 includes multiple valveassemblies such as valve assemblies S1, S2 each housed in a separatemanifold such as manifolds 20, 22. Each valve assembly S1, S2 isconnectable to a pump 12 for receiving a common inlet pump pressure andeach assembly is connectable to a separate actuator such as actuators16, 18. In certain examples, the pump 12 is a variable displacementpump. In other examples, the pump 12 is a fixed displacement pump havingan inlet pressure compensator.

A load sense compensator 14 is mounted to the pump 12 for controllingthe inlet pump pressure of the pump 12 based on a load sense pressure.The load sense compensator 14 receives a load sense pressure from a loadsense line 24 connected to a shuttle valve 26. The shuttle valve 26 isconnected to one or more work ports 42 of the valve assemblies S1, S2.The shuttle valve 26 is adapted to open in the direction of the workport having the highest load sense pressure. In some alternativeexamples, check valves can be used instead of the shuttle valve 26 to dothis function. Also, the figures depict the hydraulic system 10 ashaving two valve assemblies S1, S2, however, it is to be understood thatthe hydraulic system 10 may include more than two valve assemblies ormay include a single valve assembly.

Each valve assembly S1, S2 includes a main valve 30 connected to thepump 12 for receiving hydraulic fluid. Each main valve 30 has a variableorifice 32 whose opening is proportional to the movement of a spool 34within the main valve 30. In some examples, the position of the spool 34in the main valve 30 may be controlled by a solenoid coil 36. In otherexamples, other methods may be used to control the position of the spool34.

Each valve assembly S1, S2 includes a pressure compensator valve 50 formaintaining a constant pressure drop across the variable orifice 32 sothat output flow from the main valve 30 is dependent only on themetering orifice size created by the movement of the spool 34 within themain valve 30. The pressure compensator valve 50 has a spool 52 that ismoveable between a closed position and an opened position. In the closedposition, fluid from the variable orifice 32 of the main valve 30 isblocked. In the open position, fluid from the variable orifice 32 iscommunicated to a work port 42 connected to an actuator 16, 18.

The pressure compensator valve 50 is biased in the closed position by abiasing element 54 housed in a biasing chamber 56 and disposed at oneend of the spool 52 of the pressure compensator valve 50. A pilotsurface 58 disposed at an opposite end of the biasing element 54receives an inlet pump pressure from the pump 12 for overcoming thebiasing force of the biasing element 54 and thereby moving the pressurecompensator valve 50 from the closed position to the open position.

Still referring to FIGS. 2 and 3, each valve assembly S1, S2 is depictedas having a pressure limiter valve 60 in fluid communication with themain valve 30 and the pressure compensator valve 50 inside the manifolds20, 22. The pressure limiter valve 60 includes a spool 62 moveablebetween an open position and a closed position. In the closed position,fluid from the variable orifice 32 of the main valve 30 is blocked. Inthe open position, fluid from the pilot surface 58 of the spool 52 inthe pressure compensator valve 50 is drained to a tank 46. A biasingelement 66 is positioned next to an end of the spool 62 for biasing thespool 62 into the closed position by a threshold biasing force. Incertain examples, the biasing element 66 is a spring. The spool 62 ofthe pressure limiter valve 60 has a pilot surface 64 on an opposite endof the spool. The pilot surface 64 is adapted to receive a work portpressure from the work port 42. The spool 62 is adapted to move into theopen position when the work port pressure received by the pilot surface64 overcomes the threshold biasing force of the biasing element 66. Inthe example depicted in FIGS. 2 and 3, each pressure limiter valve 60 isa two way two position valve.

The pressure limiter valves 60 are each biased by a different thresholdrelief pressure. For example, the pressure limiter valve 60 in valveassembly S2 is biased by a threshold relief pressure (e.g., 120 bar)greater than the threshold relief pressure (e.g., 60 bar) of thepressure limiter valve 60 in valve assembly S1. The different thresholdrelief pressures are desirable depending on the characteristics of eachvalve assembly including the requirements of the actuators (e.g.,actuators 16, 18) connected to the valve assemblies.

Each valve assembly S1, S2 may operate independently of the other valveassembly such that each valve assembly may operate under a differentload sense pressure. For example, the actuator 18 connected to thesecond valve assembly S2 may be working under a load sense pressure(e.g., 100 bar) that is greater than the load sense pressure (e.g., 50bar) of the actuator 16 connected to the first valve assembly S1. In theexample depicted in FIG. 2, the load sense pressure in the second valveassembly S2 is greater than the load sense pressure in the first valveassembly S1 such that the shuttle valve 26 is positioned to communicatethe load sense pressure from the second valve assembly S2 to the loadsense line 24 and to block the load sense pressure from the first valveassembly S1 from entering the load sense line 24. The load sense line 24communicates the load sense pressure from the second valve assembly S2to the load sense compensator 14. The load sense line also communicatesthe load sense pressure from the second valve assembly S2 to the biasingchambers 56 in each valve assembly S1, S2. The inlet pump pressure fromthe pump 12 will increase as the load sense pressure in the second valveassembly S2 increases in order to match the increased demand forpressure.

Referring now to FIGS. 2 and 4, the opening and closing of the pressurelimiter valve 60 in the first valve assembly S1 is independent of theinlet pump pressure from the pump 12. The pressure limiter valve 60 inthe first valve assembly S1 will remain closed so long as the actuator16 connected to the first valve assembly S1 has a load sense pressurebelow the threshold relief pressure (e.g., 60 bar) in the first valveassembly S1. When the pressure limiter valve 60 is in the closedposition, the inlet pump pressure from the pump 12 is directed to thepilot surface 58 of the pressure compensator valve 50 for moving thepressure compensator valve 50 to the open position by overcoming thecombined force of the biasing element 54 and the load sense pressurefrom the second valve assembly S2 that is communicated to the biasingchamber 56 that houses the biasing element 54. When the pressurecompensator valve 50 is in the open position, fluid flow is communicatedto the actuator 16 connected to the first valve assembly S1.

The fluid flow to the actuator 16 connected to the first valve assemblyS1 will not be cut off even if the threshold relief pressure (e.g., 60bar) in the first valve assembly S1 is less than threshold reliefpressure (e.g., 120 bar) in the second valve assembly S2. Thus, theoperation of the actuator 16 connected to the first valve assembly S1 isnot affected by the operation of the second valve assembly S2 which maycause the inlet pump pressure to exceed the lower threshold reliefpressure (e.g., 60 bar) of the first valve assembly S1.

Referring now to FIGS. 2 and 5, when the load sense pressure from theactuator 16 exceeds the threshold relief pressure (e.g., 60 bar) of thefirst valve assembly S1, the pressure limiter valve 60 in the firstvalve assembly S1 will move to the open position. For example, the loadsense pressure from the actuator 16 detected at the work port 42 iscommunicated to the pilot surface 64 of the spool 62 in the pressurelimiter valve 60, and overcomes the biasing force of the biasing element66. When the load sense pressure overcomes the threshold relief pressureof the biasing element 66, the pressure limiter valve 60 will move tothe open position and the inlet pump pressure that is communicated tothe pilot surface 58 of the pressure compensator valve 50 will bedrained to tank 46. This causes the pressure compensator valve 50 tomove to the closed position due to the combined force of the biasingelement 54 and the load sense pressure from the second valve assembly S2communicated via the shuttle valve 26 to the biasing chamber 56. When inthe closed position, the pressure compensator valve 50 blocks fluid fromreaching the actuator 16. Thus, flow to the actuator 16 in the firstvalve assembly S1 is cut off when the load sense pressure in the firstvalve assembly S1 exceeds the threshold relief pressure.

Referring now to FIGS. 6 and 7, an alternative hydraulic system 100 inaccordance with the present disclosure may share components and featuressimilar to those describe above with regard to the hydraulic system 10depicted in FIGS. 2-5. The hydraulic system 100 may include multiplevalve assemblies such as valve assemblies C1, C2 each housed in aseparate manifold 120, 122. Each valve assembly C1, C2 is connectable toa pump 112 for receiving a common inlet pump pressure and each assemblyis connectable to a separate actuator such as actuators 116, 118. Incertain examples, the pump 112 is a variable displacement pump. In otherexamples, the pump 112 is a fixed displacement pump having an inletpressure compensator.

A load sense compensator 114 is mounted for controlling the inlet pumppressure of the pump 112 based on a load sense pressure. The load sensecompensator 114 receives a load sense pressure from a load sense line124 connected to a shuttle valve 126. The shuttle valve 126 is connectedto one or more work ports 142 of the valve assemblies C1, C2. Theshuttle valve 126 is adapted to open in the direction of the work porthaving the highest load sense pressure. In some alternative examples,check valves can be used instead of the shuttle valve 126 to do thisfunction. Also, the figures depict the hydraulic system 100 as havingtwo valve assemblies C1, C2, however, it is to be understood that thehydraulic system 100 may include more than two valve assemblies or mayinclude a single valve assembly.

Each valve assembly C1, C2 includes a main valve 130 connected to thepump 112 for receiving hydraulic fluid. Each main valve 130 has avariable orifice 132 whose opening is proportional to the movement of aspool 134 within the main valve 130. In some examples, the position ofthe spool 134 may be controlled by a solenoid coil 136. In otherexamples, other methods may be used to control the position of the spool134.

Each valve assembly C1, C2 includes a pressure compensator valve 150 formaintaining a constant pressure drop across the variable orifice 132such that output flow from the main valve 130 is dependent only on themetering orifice size created by the movement of the spool 134 withinthe main valve 130. The pressure compensator valve 150 has a spool 152moveable between a closed position and an opened position. In the closedposition, fluid from the variable orifice 132 of the main valve 130 isblocked. In the open position, fluid from the variable orifice 132 iscommunicated to a work port 142 connected to an actuator 116, 118.

The pressure compensator valve 150 is biased into the closed position bya biasing element 154 housed in a biasing chamber 156 and disposed atone end of the spool 152 of the pressure compensator valve 150. A pilotsurface 158 disposed at an opposite end of the biasing element 154receives an inlet pump pressure from the pump 112 for overcoming thebiasing force of the biasing element 154 and thereby moving the pressurecompensator valve 150 from the closed position to the open position.

Still referring to FIGS. 6 and 7, valve assembly C1 includes a pressurelimiter valve 160 in fluid communication with the main valve 130 and thepressure compensator valve 150 inside the manifold 120. The pressurelimiter valve 160 includes a spool 162 moveable between a first positionand a second position. In the first position, fluid from the variableorifice 132 of the main valve 130 flows through the pressure limitervalve 160 and towards the pilot surface 158 of the pressure compensatorvalve 150. In the second position, fluid from the pilot surface 158 ofthe pressure compensator valve 150 is drained to a tank 146. A biasingelement 166 is positioned next to an end of the spool 162 for biasingthe spool 162 into the first position by a threshold biasing force. Incertain examples, the biasing element 166 is a spring. The spool 162 hasa pilot surface 164 on an opposite side of the spool. The pilot surface164 is adapted to receive a work port pressure from the work port 142.The spool 162 is adapted to move into the second position when the workport pressure received by the pilot surface 164 overcomes the thresholdbiasing force of the biasing element 166. In the example depicted inFIGS. 6 and 7, the pressure limiter valve 160 in valve assembly C1 is athree way two position valve.

In the example depicted in FIG. 6, the valve assembly C2 has a reliefpressure valve 170 biased into a closed position by a biasing element172. The relief pressure valve 170 includes a pilot surface 174 forreceiving an inlet pump pressure from the variable orifice 132 of themain valve 130. When the inlet pump pressure exceeds the force of thebiasing element 172, the relief pressure valve 170 moves into an openposition and the inlet pump pressure is drained to tank 146. This causesthe pressure compensator valve 150 in valve assembly C2 to close due tothe combined force of the biasing element 154 and the load sensepressure that has entered into the biasing chamber 156 via the shuttlevalve 126. It is contemplated that in alternative examples the valveassembly C2 may include a pressure limiter valve 160 similar to oneincluded in valve assembly C1 or a pressure limiter valve 60 similar tothe one depicted in FIG. 2.

In the example hydraulic system 100 depicted in FIGS. 6 and 7, thepressure limiter valve 160 and the relief pressure valve 170 are biasedby different threshold relief pressures. For example, the reliefpressure valve 170 in valve assembly C2 may be biased by a thresholdrelief pressure (e.g., 120 bar) that is greater than the thresholdrelief pressure (e.g., 60 bar) of the pressure limiter valve 160 invalve assembly C1. The different threshold relief pressures may bedesirable depending on the characteristics of each valve assemblyincluding the requirements of the various actuators (e.g., actuators116, 118) that may be connected to the valve assemblies.

Each valve assembly C1, C2 may operate independently of the other valveassembly such that each valve assembly may operate under a differentload sense pressure. For example, the actuator 118 connected to thesecond valve assembly C2 may be working under a load sense pressure(e.g., 100 bar) that is greater than the load sense pressure (e.g., 50bar) of the actuator 116 connected to the first valve assembly C1. Inthe example depicted in FIG. 6, the load sense pressure in the secondvalve assembly C2 is greater than the load sense pressure in the firstvalve assembly C1 such that the shuttle valve 126 is positioned tocommunicate the load sense pressure from the second valve assembly C2 tothe load sense line 124 and to block the load sense pressure from thefirst valve assembly C1 from entering the load sense line 124. The loadsense line 124 communicates the load sense pressure from the secondvalve assembly C2 to the load sense compensator 114. The load sense line124 also communicates the load sense pressure from the second valveassembly C2 to the biasing chambers 156 in each valve assembly C1, C2.The inlet pump pressure from the pump 112 will increase as the loadsense pressure in the second valve assembly C2 increases in order tomatch the increased demand for pressure.

Referring to FIGS. 6 and 8, the movement of the pressure limiter valve160 in the first valve assembly C1 is independent of the inlet pumppressure. The pressure limiter valve 160 in the first valve assembly C1remains in the first position while the actuator 116 connected to thefirst valve assembly C1 has a load sense pressure below the thresholdrelief pressure (e.g., 60 bar). When in the first position, the inletpump pressure from the pump 112 flows through the pressure limiter valve160 toward the pilot surface 158. This moves the pressure compensatorvalve 150 to the open position by overcoming the force of the biasingelement 154 and the load sense pressure from the second valve assemblyC2 communicated to the biasing chamber 156. When the pressurecompensator valve 150 is in the open position, flow is communicated tothe actuator 116 connected to the first valve assembly C1.

The flow to the actuator 116 connected to the first valve assembly C1will not be cut off even if the threshold relief pressure (e.g., 60 bar)in the first valve assembly C1 is less than threshold relief pressure(e.g., 120 bar) in the second valve assembly C2. Thus, operation of theactuator 116 connected to the first valve assembly C1 is not affected bythe operation of the second valve assembly C2 which may cause the inletpump pressure to exceed the lower threshold relief pressure (e.g., 60bar) of the first valve assembly C1.

Referring now to FIGS. 6 and 9, when the load sense pressure from theactuator 116 exceeds the threshold relief pressure (e.g., 60 bar) of thefirst valve assembly C1, the pressure limiter valve 60 in the firstvalve assembly C1 will move to the second position. For example, theload sense pressure from the actuator 116 detected at the work port 142is communicated to the pilot surface 164 of the spool 162 in thepressure limiter valve 160, and overcomes the biasing force of thebiasing element 166. When the load sense pressure overcomes thethreshold relief pressure of the biasing element 166, the pressurelimiter valve 160 will move to the second position and the inlet pumppressure communicated to the pilot surface 158 of the pressurecompensator valve 150 will drain to tank 146. This will cause thepressure compensator valve 150 to move to the closed position due to thecombined force of the biasing element 154 and the load sense pressurefrom the second valve assembly C2 that is communicated via the loadsense line 124 to the biasing chamber 156. When in the closed position,the pressure compensator valve 150 blocks flow from reaching theactuator 116. Thus, the flow to the actuator 116 is cut off when theload sense pressure in the first valve assembly C1 exceeds the thresholdrelief pressure.

As shown in FIG. 10, the flow A in a first valve assembly S1, C1 inaccordance with the present disclosure is compared with the flow B in asecond valve assembly S2, C2 as the inlet pump pressure P from a pumpincreases. The first and second valve assemblies may be included in ahydraulic system such as the ones depicted in FIGS. 2 and 6, and thefirst valve assembly S1, C1 may have a lower threshold relief pressurethan the threshold relief pressure of the second valve assembly S2, C2.FIG. 10 illustrates that the inlet flow F remains relatively constantwhile the inlet pump pressure P of the pump increases.

The load sense pressure LA of the first valve assembly S1, C1 remainsrelatively constant as the inlet pump pressure P increases. Inaccordance with the present disclosure, the flow A in the first valveassembly S1, C1 remains relatively constant as the inlet pump pressure Pincreases even as the flow B in the second valve assembly S2, C2decreases. This is due to the flow A in the first valve assembly S1, C1being independent of the inlet pump pressure and the flow B in thesecond valve assembly S2, C2. Thus, an actuator connected to the firstvalve assembly S1, C1 is not affected by an increase in the inlet pumppressure P or the decrease in flow B to an actuator connected to thesecond valve assembly.

Referring now to FIG. 11, the pilot surface 164 of the spool 162 of thethree way two position pressure limiter valve shown in FIGS. 7-9 mayvary. In certain examples, the shape of the pilot surface 164 may beconical or rounded, as shown in FIG. 11. In other examples, the shape ofthe spool 162 may be cylindrical such that the pilot surface 164 is aflat surface. In such examples, a seating 168 may be formed in the bodyof the pressure limiter valve 160, as shown in FIG. 11. In furtherexamples, the seating 168 in the body of the pressure limiter valve 160can be reduced or avoided by adding dynamic seals 169 on spool 162. Theshape of the spool 162 as well as the body of the pressure limiter valveallow the pressure limiter valve 160 to fit within certain constraintsas may be needed or desired.

Various modifications and alterations of this disclosure will becomeapparent to those skilled in the art without departing from the scopeand spirit of this disclosure, and it should be understood that thescope of this disclosure is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A valve assembly for connecting to a pump havingload sensing functionality, the valve assembly comprising: a manifold; amain valve housed inside the manifold, the main valve having a variableorifice; a pressure compensator valve adapted to maintain a constantpressure drop across the variable orifice and to communicate fluid fromthe variable orifice to a work port; and a pressure limiter valve incommunication with the main valve and the pressure compensator valve,the pressure limiter valve being biased by a threshold relief pressureand having a pilot surface that receives a local load sense pressurefrom the work port, wherein the pressure limiter valve drains fluid fromthe pressure compensator valve to tank when the local load sensepressure overcomes the threshold relief pressure of the pressure limitervalve; wherein the pressure limiter valve maintains flow to the workport when the valve assembly is part of a hydraulic system havingmultiple valve assemblies, and when at least one other valve assembly ofthe multiple valve assemblies has a higher threshold relief pressure andis operating under a higher load sense pressure than the valve assembly.2. The valve assembly of claim 1, wherein the pressure limiter valveincludes a spool moveable between a first position and a secondposition; wherein the first position directs fluid from the variableorifice of the main valve to a pilot surface of the pressure compensatorvalve, and the second position drains fluid from the pilot surface ofthe pressure compensator valve to tank; wherein the pilot surface of thepressure limiter valve is on a first side of the spool, and a biasingelement is positioned next to an opposite second side of the spool forbiasing the spool into the first position by the threshold reliefpressure; and wherein the spool slides into the second position when thelocal load sense pressure received by the pilot surface of the pressurelimiter valve overcomes the threshold relief pressure.
 3. The valveassembly of claim 1, wherein the pressure limiter valve is a two way twoposition valve having a spool moveable between a closed position and anopen position, the spool having a pilot surface that receives the localload sense pressure as a pilot pressure; wherein the local load sensepressure moves the spool of the pressure limiter valve from the closedposition to the open position; wherein the closed position blocks fluidfrom draining to tank, and the open position drains fluid to tank. 4.The valve assembly of claim 1, wherein the pressure limiter valve is athree way two position valve having a spool moveable between a firstposition and a second position, the spool having a pilot surface thatreceives the local load sense pressure as a pilot pressure; wherein thelocal load sense pressure moves the spool of the pressure limiter valvefrom the first position to the second position; wherein the firstposition communicates fluid to a pilot surface of the pressurecompensator valve, and the second position drains fluid to tank.
 5. Thevalve assembly of claim 4, wherein the pilot surface of the pressurelimiter valve has a rounded or conical shape.
 6. A hydraulic systemcomprising multiple valve assemblies, wherein at least one valveassembly is the valve assembly of claim
 1. 7. A hydraulic systemcomprising: a pump; a load sensing compensator mounted to the pump; afirst valve assembly housed in a manifold and connected to the pump andto a first actuator, the first valve assembly adapted to communicate afirst load sense pressure to the load sensing compensator, the firstvalve assembling including: a main valve having a variable orifice; apressure compensator valve adapted to maintain a constant pressure dropacross the variable orifice and to communicate fluid from the variableorifice to a work port; and a pressure limiter valve in communicationwith the main valve and the pressure compensator valve, the pressurelimiter valve being biased by a first threshold relief pressure, andincludes a pilot surface that receives the first load sense pressurefrom the work port, wherein the pressure limiter valve drains fluid fromthe pressure compensator valve to tank when the first load sensepressure overcomes the threshold relief pressure; a second valveassembly housed in a separate manifold and connected to the pump and toa second actuator, the second valve assembly adapted to communicate asecond load sense pressure to the load sensing compensator, the secondvalve assembly including: a main valve having a variable orifice; apressure compensator valve adapted to maintain a constant pressure dropacross the variable orifice of the main valve; and a pressure reliefvalve biased by a second threshold relief pressure; wherein flow to thework port of the first valve assembly is maintained when the secondthreshold relief pressure is higher than the first threshold reliefpressure and the second load sense pressure is higher than the firstload sense pressure.
 8. The hydraulic system of claim 7, wherein thepressure limiter valve is a two way two position valve that receives thefirst load sense pressure as a pilot pressure; wherein the first loadsense pressure moves the position of the pressure limiter valve from aclosed position to an open position; wherein the closed position blocksfluid from draining to tank, and the open position drains fluid to tank.9. The hydraulic system of claim 7, wherein the pressure limiter valveis a three way two position valve that receives the first load sensepressure as a pilot pressure; wherein the first load sense pressure isadapted to move the position of the pressure limiter valve from a firstposition to a second position; wherein the first position communicatesfluid to a pilot surface of the pressure compensator valve, and thesecond position drains fluid to tank.
 10. The hydraulic system of claim9, wherein the pilot surface of the pressure limiter valve in the firstvalve assembly has a rounded or conical shape.
 11. A valve assembly forconnecting to a pump having load sensing functionality, the valveassembly comprising: a manifold; a main valve housed inside themanifold, the main valve including: a variable orifice having an openingproportional to a position of a spool inside the main valve; a pressurecompensator valve adapted to maintain a constant pressure drop acrossthe variable orifice of the main valve, the pressure compensator valveincluding: a spool being moveable between at least an open position anda closed position, the closed position blocks fluid from the variableorifice of the main valve, the open position communicates fluid from thevariable orifice to a work port, the work port adapted to connect to anactuator, the spool having a pilot surface on a first side opposite asecond side of the spool; and a biasing element positioned inside abiasing chamber next to the second side of the spool for biasing thespool into the closed position, the biasing chamber adapted to receive aload sense pressure from a second valve assembly via a load sense line,the load sense pressure applying an additional biasing force for movingthe pressure compensator valve into the closed position; and a pressurelimiter valve in fluid communication with the main valve and thepressure compensator valve, the pressure limiter valve including: aspool moveable between at least a first position and a second position,the first position directs fluid from the variable orifice of the mainvalve to the pilot surface of the spool of the pressure compensatorvalve, the second position drains fluid from the pilot surface of thespool of the pressure compensator valve to tank, the spool of thepressure limiter valve having a pilot surface on a first side of thespool opposite a second side of the spool, the pilot surface adapted forreceiving a local load sense pressure from the work port; and a biasingelement positioned next to the second side of the spool for biasing thespool into the first position by a threshold relief pressure, the spoolbeing adapted to move into the first position when the local load sensepressure received by the pilot surface overcomes the threshold reliefpressure; wherein the pressure limiter valve maintains flow to the workport when the valve assembly is part of a hydraulic system havingmultiple valve assemblies, and when at least one other valve assembly ofthe multiple valve assemblies has a threshold relief pressure that ishigher than the threshold relief pressure of the pressure limiter valve,and the at least one other valve is operating under a load sensepressure that is higher than the load sense pressure of the valveassembly.
 12. The valve assembly of claim 11, wherein the pressurelimiter valve is a two way two position valve.
 13. The valve assembly ofclaim 11, wherein the pressure limiter valve is a three way two positionvalve.
 14. The valve assembly of claim 13, wherein the pilot surface ofthe pressure limiter valve has a rounded or conical shape.
 15. Ahydraulic system comprising multiple valve assemblies, wherein at leastone valve assembly is the valve assembly of claim 11.